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• ffmpeg : nvidia gpu performance sub-optimal

  3 août 2021, par david furst

  the problem seems fairly basic : i'd like to create thumbnails from incoming video in the shortest time possible, and i'm trying to do this by offloading processing to an nvidia gpu.

  


  while i run ffmpeg, i'm monitoring the gpu usage with the nvidia-smi utility. gpu usage never goes above 15% and the amount of time to encode the thumbnails with gpu is only 10% less than the time required without the gpu. these performance levels are very disappointing.

  


  my question : am i going about this the wrong way (and if so, how should i go about it), or is this gpu performance 'normal'/'reasonable' ?

  


  SYSTEM INFORMATION

  


  the machine is a desktop pc running windows 10, 8gb ram, intel i7-7700. the gpu is an nvidia quadro pro 4000 with cuda 11.4 installed. ffmpeg is version N-101372-gb5cb8c8767-g2fc309e699+4 (2021) running under mingw, with --enable-cuda --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-libnpp --enable-nvdec and --enable-nvenc.

  


  a typical ffmpeg command line i've used is :

  


   1 ffmpeg -hide_banner \
 2     -init_hw_device cuda=cuda:0 -filter_hw_device cuda \
 3     -hwaccel_output_format cuda \
 4     -i "$infile" \
 5     -vf "hwupload_cuda,scale_npp=w=200:h=150:format=yuv420p:interp_algo=lanczos,fps=1/1,hwdownload,format=yuv420p" \
 6     -y "$outdir/%08d.png"


  


  i've varied the above by supplementing some cuda-related parameters according to posts i've read here on stackoverflow and on the nvidia transcoding guide, but haven't been able to improve performance. adding any of -hwaccel cuda, -hwaccel cuvid, -hwaccel nvenc at the beginning of line 3 results in the error :
Impossible to convert between the formats supported by the filter 'graph 0 input from stream 0:0' and the filter 'auto_scaler_0'

  


  any pointers appreciated.

  


• Prevent suspend event when streaming video via HTML video tag

  24 septembre 2014, par jasongullickson

  I seem to be having the opposite problem of most people who are streaming video using the HTML video tag ; I’m saturating the client with data.

  When playing a long video served via ffserver (webm container) everything works great but eventually the browser (Chrome in this case) will begin throwing "suspend" events. After a number of these ( 50-100), a "stalled" event will fire and playback will stop.

  I believe the problem is that once Chrome has buffered a certain amount of video it goes into "suspend" and stops downloading more data. I’ve tested this theory by throttling the speed at which video data is delivered, and if I keep the delivered frame rate close to the playback rate, I can prevent this from happening, but of course deliberately holding back server performance isn’t ideal.

  What I’m looking for is either a way to suppress this "suspend" behavior altogether, or alternatively a way to respond to the event that prevents the eventual "stalled" state.

  Presumably the browser at some point exits the "suspend" state and begins requesting data again, but I haven’t actually observed this occurring. I’m using a chain of mpeg2 -> ffmpeg -> ffserver to stream the video so if the browser is attempting to resume loading data I don’t see the request in my application. I could use a proxy or a sniffer to watch for the traffic but I would expect that maybe there is an ffserver log that can tell me the same thing ? In any event if it’s attempting to resume the download it’s failing, and there’s no indication server-side that there’s a reason for the request to fail (in fact I can pull up the same video feed from ffserver and see it playing correctly).

  So I feel like I’ve isolated this to a client-side playback issue, and one where the browser is voluntarily giving up on loading the data, but I’m not sure how to convince it to "not do that", or at least attempt to resume when it runs the buffer dry.

• How can I extract multiple non-regular segments from a video using ffmpeg on Windows ? [closed]

  19 mars 2024, par Skeeve

  I'm trying to extract some segments from a video (and optionally combine them) using ffmpeg... but I'm not getting very far.

  


  Compared to the various examples I've found here, in the ffmpeg docs and elsewhere, I don't want to extract segments at regular intervals.

  


  Gleaning some info from a number of sources, I think I can do something like :-

  


  ffmpeg -f concat -i seg.txt -c copy out_%03d.mp4


  


  ...but that doesn't seem to work, owing to a couple of issues...

  


  

  • the 'out_%03d.mp4' isn't being expanded into out_001.mp4,
out_002.mp4, etc ; and

  


  • there are various issues where the input file
specification is flagged as being 'problematic' ; see the entries at the bottom of the 'seg.txt' file...

  


  


  The contents of seg.txt :

  


  #file 'e:\tmp\video\kr.mp4' ... 
file 'KR.mp4'

inpoint  75.0
outpoint 92.0

inpoint  275.0
outpoint 300.0

inpoint  1049.0
outpoint 1082.0

# [eof]

# errors:
#[concat @ 05a6a5c0] Unsafe file name 'E:\tmp\video\kr.mp4'
#seg.txt: Operation not permitted
#seg.txt: Invalid data found when processing input


  


  Short of doing this, I can certainly do something like :

  


  ffmpeg -i kr.mp4 ^
   -c:v libx264 -pix_fmt yuv420p -r 25 -y ^
   -preset ultrafast -crf 38 ^
      -ss   75.0 -to   92.0 out_001.mp4 ^
      -ss  275.0 -to  300.0 out_002.mp4 ^
      -ss 1049.0 -to 1082.0 out_003.mp4


  


  ...but the actual commands I need to use for each segment include filter clauses, including font files/sizes, etc, as well as other switches... and by the time paths to video files/segments are included, and the cases where I might have 50+ segments to extract from one video, I'm hitting the 8,192 character limit for a command line.

  


  I'm trying to do all this on Windows 8 32-bit, currently using ffmpeg version n6.0-22-g549430e14d-20230529 under Windows' cmd.exe. I can't really use a newer ffmpeg version as I haven't found any newer 32-bit releases.

  


  I'd appreciate any pointers on how to properly invoke ffmpeg to do what I want to do... how to correctly specify the pathed input filename.. and the output file(s) filemask correctly... and how the escaping will need to be done if the ffmpeg commands are placed in a batch file.

  


  Thanks a lot.